System for restarting internal combustion engine when engine restart request occurs

ABSTRACT

In a system, a starter includes a motor for rotatably driving an output shaft with a pinion and an actuator that shifts the pinion toward a ring gear to be engaged with the ring gear. A monitor unit monitors a rotational speed of the internal combustion engine. The rotational speed of the internal combustion engine drops after an automatic control for stop of the engine. When an engine restart request occurs with the rotational speed being within a preset range during the rotational speed of the internal combustion engine dropping by the automatic control for stop of the engine, a drive unit drives the actuator to shift the pinion toward the ring gear to be engaged with the ring gear. The drive unit rotatably drives the motor with the pinion being engaged with the ring gear to thereby crank the crankshaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Applications 2008-224277,2009-54318, and 2009-121437 filed on Sep. 2, 2008, Mar. 8, 2009, and May19, 2009, respectively. This application claims the benefit of priorityfrom the Japanese Patent Applications, so that the descriptions of whichare all incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to systems for restarting internalcombustion engines when an engine restart request occurs.

BACKGROUND OF THE INVENTION

Some types of vehicles installed with an engine automatic stop-and-startsystem, such as an idle reduction control system, have been recentlydeveloped for reduction in fuel cost, in exhaust emission, and the like.Such engine automatic stop-and-start systems, an example of which isdisclosed in Japanese Patent Application Publication No. 2002-122059,are designed to automatically stop an internal combustion engineinstalled in a vehicle in response to a driver's engine stop request.After the stop of the internal combustion engine, these engine automaticstop-and-start systems are designed to cause, in response to a driver'soperation to restart the vehicle, a starter to crank the internalcombustion engine, thus restarting the internal combustion engine.

In normal starters, a pinion is shifted by an actuator toward a ringgear coupled to a crankshaft of an internal combustion engine to beengaged with the ring gear. While being meshed with the ring gear, thepinion is rotatably driven by a motor so that the crankshaft is rotated.This cranks the internal combustion engine.

Such an engine stop-and-start system is designed to, during the internalcombustion engine being decelerated in response to a driver's enginestop request, when an engine restart request occurs, wait until theengine speed becomes nearly zero, and thereafter cause the starter tocrank the internal combustion engine. For this reason, a substantialamount of time has elapsed since the occurrence of the engine restartrequest before the restart of the internal combustion engine. Theelapsed time may cause the driver to feel that the restart of theinternal combustion engine is delayed.

In order to address this problem, each of Japanese Patent ApplicationPublications No. 2005-330813 and 2002-70699 discloses an enginestop-and-start system. The disclosed engine stop-and-start system isdesigned to, during the internal combustion engine being decelerated inresponse to a driver's engine stop request, when an engine restartrequest occurs, synchronize a rotational speed of the pinion with thatof the ring gear, and thereafter engage the pinion with the ring gear tothereby cause the starter to crank the internal combustion engine.

However, the engine stop-and-start system disclosed in the PatentApplication Publications No. 2005-330813 and 2002-70699 is designed tocarry out the synchronization of the rotational speed of the pinion withthat of the ring gear and the engagement of the pinion with the ringgear independently of: a value of the rotational speed of the internalcombustion engine at the moment when the engine restart request occurs;and the behavior of the engine speed (rotational speed of the ring gear)after the occurrence of the engine automatic stop request. This,depending on at least one of the value of the rotational speed of thering gear at the occurrence of the engine restart request and thebehavior of the engine speed after the occurrence of the engineautomatic stop request, may increase noises due to the engagement of thepinion with the ring gear.

SUMMARY OF THE INVENTION

In view of the circumstances set force above, an object of an aspect ofthe present invention is to provide systems for restarting an internalcombustion engine; these systems are designed to determine a propertiming of the engagement of a pinion of a starter with a ring gear ofthe internal combustion engine according to at least one of a value of arotational speed of the ring gear at the occurrence of an engine restartrequest and the behavior of an engine speed after the occurrence of anengine automatic stop request, thus smoothly restarting the internalcombustion engine.

According to one aspect of the present invention, there is provided asystem for restarting, according to an occurrence of an engine restartrequest, an internal combustion engine that has been automaticallycontrolled for stop thereof in response to an engine automatic stoprequest. The internal combustion engine normally works to burn fueltherein to rotate a crankshaft with a ring gear attached thereto. Thesystem includes a starter provided with a motor for rotatably driving anoutput shaft with a pinion and an actuator working to shift the piniontoward the ring gear to be engaged with the ring gear. The systemincludes a monitor unit working to monitor a rotational speed of theinternal combustion engine. The rotational speed of the internalcombustion engine drops by the automatic control for stop of theinternal combustion engine. The system includes a drive unit. When theengine restart request occurs with the rotational speed being within apreset range during the rotational speed of the internal combustionengine dropping by the automatic control for stop of the internalcombustion engine, the drive unit works to: drive the actuator to shiftthe pinion toward the ring gear to be engaged with the ring gear; androtatably drive the motor with the pinion being at least partly engagedwith the ring gear to thereby crank the crankshaft of the internalcombustion engine.

The system according to the one aspect of the present inventionimmediately engages the pinion with the ring gear in response to theengine restart request, making it possible to restart the internalcombustion engine with high responsivity with respect to the enginerestart request.

According to another aspect of the present invention, there is provideda system for restarting, according to an occurrence of an engine restartrequest, an internal combustion engine that has been automaticallycontrolled for stop thereof in response to an engine automatic stoprequest. The internal combustion engine normally works to burn fueltherein to rotate a crankshaft with a ring gear attached thereto. Thesystem includes a starter provided with a motor for rotatably driving anoutput shaft with a pinion and an actuator working to shift the piniontoward the ring gear to be engaged with the ring gear. The systemincludes a monitor unit working to monitor a rotational speed of theinternal combustion engine. The rotational speed of the internalcombustion engine (ring gear) drops by the automatic control for stop ofthe internal combustion engine. The system includes an executing unitworking to:

select, based on the rotational speed of the internal combustion engineat a timing of the occurrence of the engine restart request, any one ofa first restart task and a second restart task;

execute, when the first restart task is selected, the first restart taskto thereby, rotatably drive the motor, determine whether the pinion isallowed to be rotated with the ring gear, and, after it is determinedthat the pinion is allowed to be rotated with the ring gear, drive theactuator to shift the pinion toward the ring gear to be engaged with thering gear to thereby crank the crankshaft of the internal combustionengine; and

execute, when the second restart task is selected, the second restarttask to thereby: drive the actuator to shift the pinion toward the ringgear to be engaged with the ring gear, and rotatably drive the motorwith the pinion being at least partly engaged with the ring gear tothereby crank the crankshaft of the internal combustion engine.

The system according to another aspect of the present invention selectsany one of the first restart task and the second restart task based onthe rotational speed of the ring gear at a timing of the occurrence ofthe engine restart request.

Specifically, when the rotational speed of the internal combustionengine at the timing of the occurrence of the engine restart request isrelatively high, the system determines that it is necessary to bring therotational speed of the pinion to that of the ring gear. Then, theexecuting unit of the system executes the first restart task. The firstrestart task rotatably drives the motor, and determines whether thepinion is allowed to be rotated with the ring gear. After it isdetermined that the pinion is allowed to be rotated with the ring gear,the system determines that the pinion can be smoothly meshed with thering gear. Then, the executing unit drives the actuator to shift thepinion toward the ring gear to be engaged with the ring gear to therebycrank the crankshaft of the internal combustion engine.

Thus, it is possible to prevent or reduce noises due to the engagementof the pinion with the ring gear, and reduce the delay since theoccurrence of the engine restart request to the restarting of theinternal combustion engine.

In contrast, when the rotational speed of the internal combustion engineat the timing of the occurrence of the engine restart request isrelatively low, the system determines that the pinion can be smoothlymeshed with the ring gear without bringing the rotational speed of thepinion to that of the ring gear. Then, the executing unit of the systemexecutes the second restart task. The second restart task drives theactuator to shift the pinion toward the ring gear to be engaged with thering gear, and rotatably drive the motor with the pinion being at leastpartly engaged with the ring gear to thereby crank the crankshaft of theinternal combustion engine.

Thus, the smooth engagement of the pinion with the ring gear can preventor reduce noises due to the engagement of the pinion with the ring gear,and omit the operation required to bring the rotational speed of thepinion to that of the ring gear. This accelerates the start of thecranking of the internal combustion engine by the starter to therebyimmediately restart the internal combustion engine, and reduces theamount of power consumption of the relay.

According to a further aspect of the present invention, there isprovided a system for restarting, according to an occurrence of anengine restart request, an internal combustion engine that has beenautomatically controlled for stop thereof in response to an engineautomatic stop request. The internal combustion engine normally works toburn fuel therein to rotate a crankshaft with a ring gear attachedthereto. The system includes a starter provided with a motor forrotatably driving an output shaft with a pinion and an actuator workingto shift the pinion toward the ring gear to be engaged with the ringgear. The system includes a monitor unit working to monitor a rotationalspeed of the internal combustion engine. The rotational speed of theinternal combustion engine drops by the automatic control for stop ofthe internal combustion engine. The system includes a drive unit. Whenthe rotational speed of the internal combustion engine reaches a presetspeed close to or higher than zero without the engine restart requestoccurring, the drive unit works to drive the actuator to shift thepinion toward the ring gear to be engaged with the ring gear. When theengine restart request occurs after the engagement of the pinion withthe ring gear, the drive unit rotatably drives the motor to therebycrank the crankshaft of the internal combustion engine.

This immediately cranks the ring gear in response to the occurrence ofthe engine restart request while preventing the pinion from being meshedwith the ring gear during the positive and negative oscillations of therotational speed of the internal combustion engine. This makes itpossible to prevent noises from occurring.

According to a still further aspect of the present invention, there isprovided a system for restarting, according to an occurrence of anengine restart request, an internal combustion engine that has beenautomatically controlled for stop thereof in response to an engineautomatic stop request.

The internal combustion engine normally works to burn fuel therein torotate a crankshaft with a ring gear attached thereto. The systemincludes a starter provided with a motor for rotatably driving an outputshaft with a pinion and an actuator working to shift the pinion towardthe ring gear to be engaged with the ring gear. The system includes amonitor unit working to monitor a parameter associated with a differencebetween a rotational speed of the internal combustion engine and arotational speed of the pinion. The rotational speed of the internalcombustion engine drops by the automatic control for stop of theinternal combustion engine. A behavior of the rotational speed of theinternal combustion engine positively and negatively oscillates afterthe rotational speed of the internal combustion engine has first reachedzero. The system includes a drive unit. When the engine restart requestoccurs at least one of: during the rotational speed of the internalcombustion engine dropping, and during the behavior of the rotationalspeed of the internal combustion engine positively and negativelyoscillating, after the monitored parameter has been within a presetrange, the drive unit works to drive the actuator to shift the piniontoward the ring gear to be engaged with the ring gear, and rotatablydrive the motor with the pinion being at least partly engaged with thering gear to thereby crank the crankshaft of the internal combustionengine.

This immediately cranks the ring gear in response to the occurrence ofthe engine restart request while preventing the pinion from being meshedwith the ring gear during the positive and negative oscillations of therotational speed of the internal combustion engine. This makes itpossible to prevent noises from occurring.

According to a still further aspect of the present invention, there isprovided a system for restarting, according to an occurrence of anengine restart request, an internal combustion engine that has beenautomatically controlled for stop thereof in response to an engineautomatic stop request. The internal combustion engine normally works toburn fuel therein to rotate a crankshaft with a ring gear attachedthereto. The system includes a starter provided with a motor forrotatably driving an output shaft with a pinion and an actuator workingto shift the pinion toward the ring gear to be engaged with the ringgear. The system includes a monitor unit working to monitor a parameterassociated with a difference between a rotational speed of the internalcombustion engine and a rotational speed of the pinion. The rotationalspeed of the internal combustion engine drops by the automatic controlfor stop of the internal combustion engine. A behavior of the rotationalspeed of the internal combustion engine positively and negativelyoscillates after the rotational speed of the internal combustion enginehas first reached zero. The system includes a drive unit. When theengine restart request occurs at least one of: during the rotationalspeed of the internal combustion engine dropping, and during thebehavior of the rotational speed of the internal combustion enginepositively and negatively oscillating, the drive unit works to rotatablydrive the motor to thereby rotate the pinion so that the monitoredparameter has been within a preset range, and drive the actuator toshift the pinion toward the ring gear to be engaged with the ring gearto thereby crank the crankshaft of the internal combustion engine.

This smoothly engages the pinion with the ring gear, making it possibleto prevent noises from occurring due to the engagement.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and aspects of the invention will become apparent from thefollowing description of embodiments with reference to the accompanyingdrawings in which:

FIG. 1 is a view schematically illustrating an example of the overallhardware structure of an engine starting system according to the firstembodiment of the present invention;

FIG. 2 is a timing chart schematically illustrating a relationshipbetween the behavior of an engine speed and the first to third enginerestart control modes according to the first embodiment;

FIG. 3 is a timing chart schematically illustrating driving timings ofan electromagnetic actuator and a starter motor illustrated in FIG. 1when an ECU operates in the second engine restart control mode accordingto the first embodiment;

FIG. 4A is a graph schematically illustrating the result of tests formeasurement of sound pressure levels when a ring gear and a pinion weremeshed with each other while varying the difference between therotational speed of the ring gear and that of the pinion according tothe first embodiment;

FIG. 4B is a graph schematically illustrating part of the result of thetests illustrated in FIG. 4A;

FIG. 5 is a timing chart schematically illustrating driving timings ofthe electromagnetic actuator and the starter motor when the ECU operatesin the third engine restart control mode according to the firstembodiment;

FIG. 6 is a flowchart schematically illustrating an engine restart,control subroutine according to the first embodiment;

FIG. 7 is a flowchart schematically illustrating an engine restartcontrol subroutine according to a second embodiment of the presentinvention;

FIG. 8 is a timing chart schematically illustrating a relationshipbetween the behavior of the engine speed and the first to fourth enginerestart control modes according to a third embodiment of the presentinvention;

FIG. 9 is a flowchart schematically illustrating an engine restartcontrol subroutine according to the third embodiment;

FIG. 10 is a timing chart schematically illustrating driving timings ofthe electromagnetic actuator and the starter motor when the ECU operatesin the fourth engine restart control mode according to a fourthembodiment of the present invention;

FIG. 11 is a flowchart schematically illustrating an engine restartcontrol subroutine according to the fourth embodiment;

FIG. 12 is a timing chart schematically illustrating a relationshipbetween the behavior of the engine speed and the second and third enginerestart control modes according to a fifth embodiment of the presentinvention;

FIG. 13 is a flowchart schematically illustrating an engine restartcontrol subroutine according to the fifth embodiment; and

FIG. 14 is a flowchart schematically illustrating a part of an enginerestart control subroutine according to a modification of each of thefirst to fifth embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention will be described hereinafter withreference to the accompanying drawings. In the drawings, identicalreference characters are utilized to identify identical correspondingcomponents.

First Embodiment

An engine starting system 1 for an internal combustion engine 21installed in a vehicle according to the first embodiment of the presentinvention will be described hereinafter with reference to FIGS. 1 to 6.The internal combustion engine, referred to simply as “engine”, 21 has acrankshaft 22 with one end on which a ring gear 23 is mounted.

The engine 21 works to burn fuel within each cylinder thereof to therebychange the fuel energy to mechanical energy, such as rotative energy tothereby rotate the crankshaft 22. The rotation of the crankshaft 22 istransferred to driving wheels through a powertrain installed in thevehicle to thereby drive the vehicle.

In the vehicle, for controlling the engine 21, an ignition system 53 anda fuel injection system 55 are installed.

The ignition system 53 includes actuators, such as igniters, AC andcauses the actuators AC to provide an electric current or spark toignite an air-fuel mixture in each cylinder of the engine 21, thusburning the air-fuel mixture.

The fuel injection system 55 includes actuators, such as fuel injectors,AC and causes the actuators AC to spray fuel either directly into eachcylinder of the engine 21 or into an intake manifold (or intake port)just ahead of each cylinder thereof to thereby burn the air-fuel mixturein each cylinder of the engine 21.

In addition, in the vehicle, for slowing down or stopping the vehicle, abrake system 57 is installed.

The brake system 57 includes, for example, disc or drum brakes asactuators AC at each wheel of the vehicle. The brake system 57 isoperative to send, to each of the brakes, a deceleration signalindicative of a braking force to be applied from each brake to acorresponding one of the wheels in response to a brake pedal of thevehicle being depressed by the driver. This causes each brake to slowdown or stop the rotation of a corresponding one of the wheels of thevehicle based on the sent deceleration signal.

Reference numeral 61 represents a hand-operable shift lever (selectlever). When the vehicle is a manual transmission vehicle, the drivercan change a position of the shift lever 61 to shift (change) atransmission gear ratio of the powertrain to thereby control the numberof revolutions of the driving wheels and the torque generated by theengine 21 to the driving wheels. When the vehicle is an automatictransmission vehicle, the driver can change a position of the shiftlever 61 to shift one of the drive ranges corresponding to atransmission gear ratio of the powertrain, such as Reverse range,Neutral range, Drive range, and the like.

In addition, in the vehicle, for measuring the operating conditions ofthe engine 21 and the driving conditions of the vehicle, sensors 59 areinstalled in the vehicle.

Each of the sensors 59 is operative to measure an instant value of acorresponding one parameter associated with the operating conditions ofthe engine 21 and/or the vehicle and to output, to the ECU 20, dataindicative of the measured value of a corresponding one parameter.

Specifically, the sensors 59 include, for example, an accelerator sensor(throttle position sensor) and a brake sensor electrically connected tothe ECU 20.

The accelerator sensor is operative to:

measure an actual position or stroke of a driver-operable acceleratorpedal of the vehicle linked to a throttle valve for controlling theamount of air entering the intake manifold; and

output, as data representing a driver's starting request, accelerationrequest, or deceleration request, for the engine 21, the measured actualstroke or position of the accelerator pedal.

The brake sensor is operative to measure an actual position or stroke ofthe brake pedal of the vehicle operable by the driver and to output, asdata representing a driver's deceleration request, the measured actualstroke or position of the brake pedal.

The engine starting system 1 includes a starter 11, a battery 18, arelay 19, an ECU (Electronic Control System) 20, a switching element 24,and a relay 25.

The starter 11 is provided with a starter motor 12, a pinion 13, aone-way clutch 51, and an electromagnetic actuator 14. The one-wayclutch 51 can be omitted.

The starter motor 12 has an output shaft 12 a and an armature 12 bcoupled thereto and operative to rotate the output shaft 12 a when thearmature 12 b is energized.

The one-way clutch 51 is provided in helical spline engagement with anouter circumference of one end of the output shaft 12 a.

The pinion 13 is mounted on the one-way clutch 51 around the outercircumferential of the output shaft 12 a to be shiftable together withthe one-way clutch 51 in an axial direction of the output shaft 12 a.

The starter motor 12 is arranged opposing the engine 21 such that theshift of the pinion 13 in the axial direction of the output shaft 12 atoward the engine 21 allows the pinion 13 to abut on the ring gear 23 ofthe engine 21.

The electromagnetic actuator, referred to simply as “actuator”, 14 ismade up of a plunger 15, a solenoid 16, and a shift lever 17. Theplunger 15 is so arranged in parallel to the axial direction of theoutput shaft 12 a of the starter motor 12 as to be shiftable in itslength direction parallel to the axial direction of the output shaft 12a.

The solenoid 16 is arranged to surround the plunger 15. One end of thesolenoid 16 is electrically connected to a positive terminal of thebattery 18 via the relay 19, and the other end thereof is grounded. Theshift lever 17 has a one and the other end in its length direction. Theone end of the shift lever 17 is pivotally coupled to one end of theplunger 15, and the other end thereof is coupled to the one-way clutch51. The shift lever 17 is pivoted about a pivot located at itssubstantially center in the length direction.

The solenoid 16 works to shift the plunger 15 thereinto in its lengthdirection so as to pull it thereinto against the force of return spring(not shown) when energized. The pull-in shift of the plunger 15 pivotsthe shift lever 17 clockwise in FIG. 1 whereby the pinion 13 is shiftedtoward the ring gear 23 of the engine 21 via the shift lever 17. Thisallows the pinion 13 to be meshed with the ring gear 23 for cranking theengine 21. When the solenoid 16 is deenergized, the return springreturns the plunger 15 and the shift lever 17 to their originalpositions illustrated in FIG. 1 so that the pinion 13 is pulled-out ofmesh with the ring gear 23.

The relay 19 is designed as a mechanical relay or a semiconductor relay.The relay 19 has first and second terminals (contacts) electricallyconnected to the positive terminal of the battery 18 and the one end ofthe solenoid 16, respectively, and a control terminal electricallyconnected to the ECU 20.

For example, when an electric signal indicative of switch-on of therelay 19 is sent from the ECU 20, the relay 19 establishes electricconduction between the first and second terminals to thereby allow thebattery 18 to supply a DC (Direct Current) battery voltage to thesolenoid 16.

Otherwise, when an electric signal indicative of switch-off of the relay19 in on state is sent from the ECU 20, the relay 19 interrupts theelectric conduction between the first and second terminals to therebydisconnect the battery 18 from the solenoid 16.

The relay 25 is designed as, for example, a mechanical relay. Forexample, the relay 25 includes a solenoid 25 a and a switch 25 b. Theswitch 25 b is electrically connected between the positive terminal ofthe battery 18 and the armature 12 b of the starter motor 12. The switch25 b is turned on by magnetic force generated when the solenoid 25 a isenergized, thus establishing electrical conduction between the armature12 a and the battery 18. This turns the armature 12 b of the startermotor 12 to thereby rotatably drive the pinion 13.

The switching element 24 has first and second terminals electricallyconnected to the positive terminal of the battery 18 and the solenoid 25a, respectively, and a control terminal electrically connected to theECU 20.

For example, when an electric signal, such as a pulse current with apulse width (pulse duration) corresponding to the energization duration(on period) of the switching element 24, is sent from the ECU 20, theswitching element 24 establishes, during on period of the pulse current,electric conduction between the first and second terminals to therebyallow the battery 18 to supply the battery voltage to the solenoid 25 ato energize it.

The switching element 24 also interrupts, during on period of the pulsecurrent, the electric conduction between the first and second terminalsto thereby disconnect the battery 18 from the solenoid 25 a. A dutycycle of the starter motor 12 is represented as a ratio of the on period(pulse width) of the pulse current to the repetition interval (sum ofthe on and off periods) thereof.

The ECU 20 is designed as, for example, a normal microcomputer circuitconsisting of, for example, a CPU, a storage medium 20 a including a ROM(Read Only Memory), such as a rewritable ROM, a RAM (Random AccessMemory), and the like, an IO (Input and output) interface, and so on.

The storage medium 20 a stores therein beforehand various engine controlprograms.

The ECU 20 is operative to:

receive pieces of data measured by the sensors 59 and sent therefrom;and

control, based on the operating conditions of the engine 21 determinedby at least some of the received pieces of data measured by the sensors59, various actuators AC installed in the engine 21 to thereby adjustvarious controlled variables of the engine 21.

Specifically, the ECU 20 is programmed to:

compute a proper ignition timing for the igniter AC for each cylinder, aproper fuel injection timing and a proper injection quantity for thefuel injector AC for each cylinder;

instruct the igniter AC for each cylinder to ignite an air-fuel mixturein each cylinder at a corresponding computed proper ignition timing; and

instruct the fuel injector AC for each cylinder to spray, at acorresponding computed proper injection timing, a corresponding computedproper quantity of fuel into each cylinder.

In addition, the engine control programs stored in the storage medium 20a include an engine automatic stop-and-start routine (program) R1. TheECU 20 repeatedly runs the engine automatic stop-and-start routine R1 ina given cycle during its being energized to carry out an engineautomatic stop-and-start control task T, in other words, idle reductioncontrol task T.

Specifically, in accordance with the engine automatic stop- and startcontrol routine R1, the ECU 20 repetitively determines whether an engineautomatic stop request occurs based on the data measured by the sensors59.

When the driver operates the accelerator pedal to fully close thethrottle valve or operates the brake pedal to thereby send adeceleration request to the ECU 20 during the vehicle running, the ECU20 detects the driver's deceleration request operation based on the datameasured by the accelerator sensor or the brake sensor. Then, the ECU 20determines that the engine automatic stop request occurs. Moreover, whenthe vehicle is stopped, the ECU 20 determines that the engine automaticstop request occurs.

Then, the ECU 20 carries out an automatic stop control of the engine 21.Specifically, the ECU 20 controls the ignition system 53 and/or the fuelinjection system 55 to stop the burning of the air-fuel mixture in eachcylinder. The stop of the burning of the air-fuel mixture in eachcylinder of the engine 21 means the automatic stop of the engine 21.

After the automatic stop of the engine 21, in accordance with the engineautomatic stop- and start control routine R1, the ECU 20 determineswhether an engine restart request occurs based on the data measured bythe sensors 59 and data inputted from another device installed in thevehicle.

When the engine automatic stop request is released during the vehiclerunning, for example, the throttle valve is shifted from the fully closeposition, the ECU 20 determines that the engine restart request occurs.Moreover, when the driver, for example, releases the brake pedal oroperates the shift lever 61 in preparation to the restart of the vehicleduring the vehicle being stopped, the ECU 20 determines that the enginerestart request occurs. In addition, the driver, for example, depressesthe accelerator pedal to restart the vehicle, the ECU 20 determines thatthe engine restart request occurs. Then, the ECU 20 runs an enginerestart control subroutine R2 included in the engine automatic stop- andstart control routine R1 and described hereinafter to therebyautomatically restart the engine 21.

Specifically, referring to FIG. 2, the ECU 20 is programmed to selectone of predetermined first to third restart control modes based on aspeed Ne of the engine 20 in rpm (revolution per minute), referred tosimply as “engine speed”, after the automatic stop of the engine 21.

After the automatic stop of the engine 21, the ECU 20 monitors theengine speed Ne using a map.

In the first embodiment, the storage medium 20 a of the ECU 20 storestherein a map M1 designed as, for example, a data table or a program.The map M1 represents a function (relationship) between a variable ofthe engine speed Ne and a variable of the elapsed time since theoccurrence of the engine automatic stop request. The function can havebeen determined based on data obtained by tests using the engine 21 orits computer model. The function also can have been determined based ondesign data of the engine 21. The function usually represents that theengine speed Ne is reduced with increase in the elapsed time since theoccurrence of the engine automatic stop request.

Specifically, the ECU 20 measures the elapsed time since the occurrenceof the engine automatic stop request using, for example, at least onetimer or at least one counter installed in the CPU. The ECU 20references the map M1 using, as a key, the measured value of the elapsedtime since the occurrence of the engine automatic stop request. Based ona result of the reference, the ECU 20 retrieves a value of the enginespeed Ne corresponding to the measured value of the elapsed time sincethe occurrence of the engine automatic stop request, thus monitoring theengine speed Ne.

Referring to FIG. 2, after the automatic stop of the engine 21 inresponse to the occurrence of the engine automatic stop request, theengine speed Ne linearly drops over a period of time, referred to as“engine-speed drop period”. When the engine speed Ne reaches zerocorresponding the end of the engine-speed drop period, the behavior ofthe engine speed Ne oscillates in the direction of its normal positiverotation and its negative rotation over a period of time, referred to as“engine-speed oscillation period”. After the engine-speed oscillationperiod, the engine speed Ne becomes zero so that the engine 21 iscompletely stopped. The negative oscillation of the engine speed is dueto the compression pressure in each cylinder immediately before thecompression top dead center (TDC). If the pinion 13 were tried to beengaged with the ring gear 23 during the engine speed Ne (rotationalspeed of the ring gear 23) positively and negatively oscillating, thepinion 13 would hit the negatively oscillating ring gear 23. This wouldcause a large impact on the pinion 13, and therefore, would damage thepinion 13 (starter 12) and cause high level noises.

Date indicative of the waveform of the behavior of the engine speed Neafter the automatic stop of the engine 21 including the engine-speeddrop period and the engine-speed oscillation period of the engine 21 hasbeen measured by tests using the engine 21 or its computer model. Thedata has been stored in the storage medium 20 a of the ECU 20.

During the engine-speed drop period by the automatic stop of the engine21, when the engine restart request occurs with the monitored enginespeed Ne being within a first speed range RA1 higher than a first presetspeed N1, such as 500 rpm, the ECU 20 determines that the engine 20 isallowed to be restarted without cranking by the starter 11.

Thus, the ECU 20 shifts its operation mode to the first restart controlmode, and carries out a first restart control task in the first restartcontrol mode.

Specifically, in the first restart control mode, the ECU 20 controls theignition system 53 and/or the fuel injection system 55 to restart theignition and/or the fuel-injection for each cylinder without crankingthe crankshaft 22 by the starter 11, thus automatically restarting theengine 21.

This achieves an advantage of restarting the burning of the air-fuelmixture in each cylinder of the engine 21 in immediate response to theoccurrence of the engine restart request to thereby immediately restartthe engine 21. In addition, because the need for cranking the engine 21is eliminated, it is possible to eliminate the power consumption of thestarter 11, and the need for the engagement of the pinion 13 with thering gear 23 with the difference between their rotational speeds beinghigh, thus preventing or reducing noises and impacts from occurring dueto the rotational speed difference.

During the engine-speed drop period by the automatic stop of the engine21, when the engine restart request occurs with the monitored enginespeed Ne being within a second speed range RA2 equal to or lower thanthe first preset speed N1 and higher than a second preset speed N2, suchas 250 rpm, the ECU 20 determines that the pinion 13 is not smoothlymeshed with the ring gear 23 until the rotational speed of the pinion 13becomes close to that of the ring gear 23. This is because the RPM ofthe ring gear 23 is relatively high.

Thus, the ECU 20 shifts its operation mode to the second restart controlmode, and carries out a second restart control task in the secondrestart control mode.

Specifically, in the second restart control mode, the ECU 20 drives theswitching element 24 to turn it on, thus energizing the solenoid 25 a.This rotatably drives the starter motor 12 to thereby rotate the pinion13.

The ECU 20 monitors the rotational speed of the pinion 13 using a map.In the first embodiment, the storage medium 20 a of the ECU 20 storestherein a map M2 designed as, for example, a data table or a program.

The map M2 represents a variable of the rotational speed of the pinion13 as a function of: the elapsed time (energization duration) since thestart of the energization of the starter motor 12, and the amount ofcurrent to be applied to the starter motor 12 (switching element) 24,such as the duty cycle of the PWM signal to be applied to the switchingelement 24. The function can have been determined based on data obtainedby tests using the engine starting system 1 or its computer model. Thefunction also can have been determined based on design data of theengine starting system 1. The function usually represents that therotational speed of the starter motor 12 is increased with increase inthe elapsed time since the start of the energization of the startermotor 12 and with increase in the current to be applied to the startermotor 12.

Specifically, the ECU 20 measures the elapsed time since the start ofthe energization of the starter motor 12 using, for example, the atleast one timer or the at least one counter installed in the CPU. TheECU 20 references the map M2 using, as a key, the measured value of theelapsed time since the start of the energization of the starter motor 12and the duty cycle of the starter motor 12. Based on a result of thereference, the ECU 20 retrieves a value of the rotational speed of thepinion 13 corresponding to the measured value of the elapsed time sincethe start of the energization of the stator motor 12 and the duty cyclethereof, thus monitoring the rotational speed of the pinion 13.

Thereafter, when the monitored rotational speed of the pinion 13 becomesclose to that of the ring gear 23, the ECU 20 drives the electromagneticactuator 14 to shift the rotating pinion 13 toward the ring gear 23 sothat the rotating pinion 13 is meshed with the ring gear 23. Theengagement of the rotating pinion 13 with the ring gear 23 cranks thecrankshaft 22 of the engine 21 to thereby restart the engine 21.

More specifically, referring to FIG. 3, when the engine restart requestoccurs at time t1 with the monitored engine speed Ne being within thesecond speed range RA2, the ECU 20 shifts its operation mode to thesecond restart control mode, and rotatably drives the starter motor 12to thereby rotate the pinion 13.

Thereafter, the ECU 20 monitors the difference in rotational speedbetween the ring gear 23 and the pinion 13, and when the monitoreddifference in rotational speed between the ring gear 23 and the pinion13 falls within a range of ±250 rpm, preferably ±200 rpm, at time 12,the ECU 20 determines that the rotational speed of the pinion 13 becomesclose to that of the ring gear 23. In other words, when the monitoreddifference in rotational sped between the ring gear 23 and the pinion 13falls within a range of ±250 rpm, preferably ±200 rpm, at time t2, theECU 20 determines that the pinion 13 is allowed to rotate with the ringgear 23 when the pinion 13 abuts on the ring gear 23.

Then, the ECU 20 drives the electromagnetic actuator 14 to shift therotating pinion 13 toward the ring gear 23 so that the rotating pinion13 abuts on the ring gear 23 and thereafter is meshed with the ring gear23. The engagement of the rotating pinion 13 with the ring gear 23cranks the crankshaft 22 of the engine 21 to thereby restart the engine21.

Note that the difference in rotational speed between the ring gear 23and the pinion 13 means the difference in rotational speed between thering gear 23 and the pinion 13 when the rotational speed of the pinion13 is corrected such that a diameter of an addendum circle of the ringgear 23 is in agreement with that of the addendum circle of the pinion13.

The engine restart operations in the second restart control mode reducethe delay from the occurrence of the engine restart request to therestart of the engine 21 while smoothly engaging the pinion 13 with thering gear 23 to thereby prevent or reduce noises and impacts due to theengagement.

In addition, because it is unnecessary to completely synchronize therotational speed of the pinion 13 with the rotational speed of the ringgear 23 in order to engage the pinion 13 with the ring gear 23, themeasurement accuracy of the rotational speeds of the pinion 13 and thering gear 23 need not be high. Thus, as described above, the rotationalspeed of the ring gear 23 and the rotational speed of the pinion 13 canbe measured by the computer estimations based on the maps in place of acrank angle sensor for measuring the rotational speed of the ring gear23 and a rotational speed sensor for measuring the rotational speed ofthe pinion 13. Because the crank angle sensor and the rotational anglesensor are expensive, the engine starting system 1 meets the low-costrequirements for vehicles as recent important technical requirements.

For example, in the first embodiment, the diameter of the addendumcircle of the ring gear 23 is set to 300 mm, and the diameter of theaddendum circle of the pinion 13 is set to 30 mm. Thus, when therotational speed of the ring gear 23 is 300 rpm and the rotational speedof the pinion 13 is 1000 rpm, the difference between the rotationalspeed of the ring gear 23 and the corrected rotational speed of thepinion 13 is calculated as 200 rpm.

Because the diameter of the addendum circle of the ring gear 23 is 300mm and the rotational speed thereof is 300 rpm, a peripheral speed on apitch circle of the ring gear 23 becomes approximately 4.7 meters persecond. Note that the pitch circle of the ring gear 23 represents animaginary circle that is made rolling contact with the gear of thepinion 13.

Similarly, because the diameter of the addendum circle of the pinion 13is 30 mm and the rotational speed thereof is 1000 rpm, a peripheralspeed on a pitch circle of the pinion 13 becomes approximately 1.6meters per second. Note that the pitch circle of the pinion 13represents an imaginary circle that is made rolling contact with thering gear 23.

From the viewpoint, the difference between the peripheral speed on thepitch circle of the ring gear 23 and that on the pitch circle of thepinion 13 becomes approximately 3.1 meters per second. Thus, the factthat the difference between the rotational speed of the ring gear 23 andthat of the pinion 13 becomes within 200 rpm means the fact that thedifference between the peripheral speed on the pitch circle of the ringgear 23 and that on the pitch circle of the pinion 13 becomes within±3.1 meters per second.

The inventors of the present application carried out tests formeasurement of sound pressure levels when the ring gear 23 and thepinion 13 were meshed with each other while varying the differencebetween the rotational speed of the ring gear 23 and that of the pinion13.

Specifically, the inventors measured a sound pressure level when thering gear 23 with the diameter of its addendum circle of 300 mm and thepinion 13 with the diameter of its addendum circle of 30 mm were meshedwith each other for each value of the varied differences between therotational speed of het ring gear 23 and that of the pinion 13. Thesound pressure level when the ring gear 23 and the pinion 13 were meshedwith each other was measured with a microphone located at a distance of15 cm from the meshed position.

FIGS. 4A and 4B show the result of the tests in graph format. Thehorizontal axis of each of FIGS. 4A and 4B represents the differencebetween the rotational speed of het ring gear 23 and that of the pinion13 in rpm, and the vertical axis represents the measured sound pressurelevel in dB.

Each of the positive values of the varied differences in RPM between thering gear 23 and the pinion 13 represent that the ring gear 23 is higherthan that of the pinion 13 in rpm, and each of the negative values ofthe varied differences in RPM between the ring gear 23 and the pinion 13represent that the ring gear 23 is lower than that of the pinion 13 inrpm. FIG. 4B particularly illustrates the result of the tests for eachof the positive values of the varied differences in RPM between the ringgear 23 and the pinion 13.

FIGS. 4A and 4B demonstrate, that, when the difference between therotational speed of het ring gear 23 and that of the pinion 13 ismaintained within ±250 rpm, preferably within ±200 rpm, the soundpressure levels at the engagement of the pinion 13 with the ring gear 23are sufficiently reduced. In other words, FIGS. 4A and 4B demonstratethat, when the difference between the peripheral speed of het ring gear23 and that of the pinion 13 is preferably maintained within ±3.1 metersper second, the sound pressure levels at the engagement of the pinion 13with the ring gear 23 are sufficiently reduced.

In the first embodiment, referring to FIG. 1, the starter 11 isconfigured such that the one-way clutch 51 is provided in helical splineengagement with the outer circumference of the one end of the outputshaft 12 a. The one-way clutch 51 works to transfer rotational motionsupplied from the starter motor 12 to the pinion 13 without transferringrotational motion supplied from the pinion 13 to the starter motor 12.

The ECU 20 according to the first embodiment can be modified todetermine that the pinion 13 is allowed to rotate with the ring gear 23when the pinion 13 abuts on the ring gear 23 when:

the rotational speed of the ring gear 23 is higher than that of thepinion 13; and

the difference in rotational speed between the ring gear 23 and thepinion 13 is equal to or lower than a preset value of, for example, 200rpm.

As described above, the fact that difference in rotational speed betweenthe ring gear 23 and the pinion 13 is equal to or lower than 200 rpmmeans the fact that the difference between the peripheral speed on thepitch circle of the ring gear 23 and that on the pitch circle of thepinion 13 is equal to or lower than 3.1 meters per second.

With the configuration of the modified ECU 20, it is possible to reducethe impact caused when the pinion 13 abuts on the ring gear 23 becausethe one-way clutch 51 idles. Thereafter, friction between the ring gear23 and the pinion 13 gradually reduces the RPM of the ring gear 23 withincrease in the RPM of the pinion 13 so that the pinion 13 is meshedwith the ring gear 23.

When the difference in rotational speed between the ring gear 23 and thepinion 13 becomes substantially zero, the one-way clutch 51 is locked sothat the one-way clutch 51 starts the transfer of the rotational motionsupplied from the ring gear 23 to the pinion 13. The actions of thepinion 13, the one-way clutch 51, and the ring gear 23 allow the pinion13 to be smoothly meshed with the ring gear 23. Thus, the impact on theelements of the starter 11 due to the engagement of the pinion 13 withthe ring gear 23 is reduced, making it possible to give enough strengthto the elements of the starter 11.

During the engine-speed drop period by the automatic stop of the engine21, when the engine restart request occurs with the monitored enginespeed Ne being within a third speed range RA3 equal to or lower than thesecond preset speed N2 and higher than a third preset speed N3, the ECU20 determines that the pinion 13 is allowed to be smoothly meshed withthe ring gear 23 without bringing the rotational speed of the pinion 13closer to that of the ring gear 23. This is because the RPM of the ringgear 23 is relatively low.

Thus, the ECU 20 shifts its operation mode to the third restart controlmode, and carries out a third restart control task in the third restartcontrol mode.

Specifically, in the third restart control mode, the ECU 20 drives theelectromagnetic actuator 14 to shift the rotating pinion 13 toward thering gear 23 so that the rotating pinion 13 is meshed with the ring gear23. After or during the engagement of the pinion 13 with the ring gear23, the ECU 20 drives the switching element 24 to turn it on, thusenergizing the solenoid 25 a. This rotatably drives the starter motor 12to rotate the pinion 13. This cranks the crankshaft 22 of the engine 21to thereby restart the engine 21.

More specifically, referring to FIG. 5, when the engine restart requestoccurs at time t3 with the monitored engine speed Ne being within thethird speed range RA3, the ECU 20 shifts its operation mode to the thirdrestart control mode, and drives the electromagnetic actuator 14 toshift the pinion 13 toward the ring gear 23 so that the pinion 13 abutson the ring gear 23 and thereafter is meshed with the ring gear 23.

At the point of time t4 when the engagement of the pinion 13 with thering gear 23 has been completed or during the engagement of the pinion13 with the ring gear 23, the ECU 20 rotatably drives the starter motor12 to thereby rotate the pinion 13. This cranks the crankshaft 22 of theengine 21 to thereby restart the engine 21.

The engine restart operations in the third restart control mode omit theoperations to bring the rotational speed of the pinion 13 closer to thatof the ring gear 23 while smoothly engaging the pinion 13 with the ringgear 23 to thereby prevent or reduce noises and impacts due to theengagement. The omission of the operations to bring the rotational speedof the pinion 13 closer to that of the ring gear 23 immediately startsthe cranking of the crankshaft 22 by the starter 11 so as to immediatelyrestart the engine 21 with reduction in the power consumption of thestarter 11.

Next, an engine restart control task to be executed by the ECU 20 inaccordance with the engine restart control subroutine R2 will bedescribed hereinafter with reference to FIG. 6. The engine restartcontrol subroutine R2 is repeatedly called in a given cycle duringexecution of the engine automatic stop-and-start control routine R1.

When the engine restart control subroutine R2 is called, the ECU 20determines whether the engine 21 is under the automatic stop control instep 101. In other words, the ECU 20 determines whether the calledtiming is before the occurrence of the engine restart request and afterthe stop of burning of the air-fuel mixture in each cylinder in step101.

Upon determining that the engine 21 is not under the automatic stopcontrol (NO in step 101), the ECU 20 exits the engine restart controlsubroutine R2 without executing the following steps 102 to 110, andreturns to the main routine R1.

Otherwise, upon determining that the engine 21 is under the automaticstop control (YES in step 101), the ECU 20 determines whether the enginerestart request occurs in step 102.

Upon determining that no engine restart requests occur (NO in step 102),the ECU 20 exits the engine restart control subroutine R2, and returnsto the main routine R1.

Otherwise, upon determining that the engine restart request occurs (YESin step 102), the ECU 20 proceeds to step 103.

In step 103, the ECU 20 determines whether the engine speed Ne is higherthan the first preset speed N1 to thereby determine whether the enginespeed Ne is within the first speed range RA1.

The first preset speed N1 can be selected from, for example, the rangeof 300 to 700 rpm, and, in the first embodiment, is set to 500 rpm setforth above. During the engine-speed drop period by the automatic stopof the engine 21, when the engine speed Ne is higher than the firstpreset speed N1 selected from the range of 300 rpm to 700 rpm, restartof the burning of the air-fuel mixture in each cylinder by the ignitionand/or the fuel-injection allows the engine 21 to restart withoutcranking the crankshaft 22 by the starter 11.

That is, the first speed range RA1 higher than the first preset speed N1selected from the range of 300 rpm to 700 rpm is a range in which therestarting of the ignition and/or the fuel-injection for each cylinderwithout cranking the crankshaft 22 by the starter 11 allows the engine21 to be restarted.

Specifically, when it is determined that the engine speed Ne is higherthan the first preset speed N1 so that the engine restart request occurswith the engine speed Ne being within the first speed range RA1 (YES instep 103), the ECU 20 determines that the engine 20 is allowed to berestarted without cranking by the starter 11.

Thus, the ECU 20 shifts its operation mode to the first restart controlmode and carries out the first restart control task in step 104.

Specifically, in step 104, the ECU 20 controls the ignition system 53and/or the fuel injection system 55 to restart the ignition and/or thefuel-injection for each cylinder without cranking the crankshaft 22 bythe starter 11, thus automatically restarting the engine 21 in step 104a.

Thereafter, in step 105, the ECU 20 determines whether the restart ofthe engine 21 has been completed. For example, in step 105, the ECU 20determines whether the engine speed Ne exceeds a preset speed fordetermination of restart completion. Upon determining that the enginespeed Ne does not exceed the preset speed for determination of restartcompletion (NO in step 105), the ECU 20 determines that the restart ofthe engine 21 has not been completed yet. Then, the ECU 20 returns tostep 103, and repeatedly carries out the operations in steps 103 to 105until the determination in step 103 is NO or the determination in step105 is YES.

When the determination in step 105 is YES, the ECU 20 determines thatthe restart of the engine 21 has been completed, and therefore, exitsthe engine restart control subroutine R2.

Otherwise, when it is determined that the engine speed Ne is equal to orlower than the first preset speed N1 (NO in step 103), the ECU 20proceeds to step 106. In step 106, the ECU 20 determines whether theengine speed Ne is higher than the second preset speed N2 to therebydetermine whether the engine speed Ne is within the second speed rangeRA2 or the third speed range RA3.

The second preset speed N2 can be selected from, for example, the rangeof 50 rpm to 450 rpm, and, in the first embodiment, is set to 250 rpmset forth above. During the engine-speed drop period by the automaticstop of the engine 21, when the engine speed Ne is equal to or lowerthan the second preset speed N2 selected from the range of 50 rpm to 450rpm, the pinion 13 can be smoothly meshed with the ring gear 23 withoutthe rotational speed of the pinion 13 being brought closer to that ofthe ring gear 23.

That is, the third speed range RA3 equal to or lower than the secondpreset speed N2 selected from the range of 50 rpm to 450 rpm is a rangein which the pinion 13 is allowed to be smoothly engaged with the ringgear 23 without the rotational speed of the pinion 13 being broughtcloser to that of the ring gear 23.

Upon determining that the engine speed Ne is higher than the secondpreset speed N2 so that the engine restart request occurs with theengine speed Ne being within the second speed range RA2 (YES in step106), the ECU 20 determines that the pinion 13 is not smoothly meshedwith the ring gear 23 until the rotational speed of the pinion 13becomes close to that of the ring gear 23 because the RPM of the ringgear 23 is relatively high. Then, the ECU 20 proceeds to step 107,shifts its operation mode to the second restart control mode, andcarries out the second restart control task in step 107.

Specifically, the ECU 20 rotatably drives the starter motor 12 tothereby rotate the pinion 13 in step 107 a.

After the difference in rotational speed between the ring gear 23 andthe pinion 13 falls within a range of ±250 rpm, preferably ±200 rpm sothat the monitored rotational speed of the pinion 13 becomes close tothat of the ring gear 23, the ECU 20 drives the electromagnetic actuator14 to shift the rotating pinion 13 toward the ring gear 23 so that therotating pinion 13 is meshed with the ring gear 23 in step 107 b. Theengagement of the rotating pinion 13 with the ring gear 23 cranks thecrankshaft 22 of the engine 21 to thereby restart the engine 21.

Next, the ECU 20 proceeds to step 108, and determines whether therestart of the engine 21 has been completed in step 108 in the samemanner as step 105.

Upon determining that the restart of the engine 21 has been completed(YES in step 108), the ECU 20 exits the engine restart controlsubroutine R2 and returns to the main routine R1.

Otherwise, upon determining that the engine speed Ne does not exceed thepreset speed for determination of restart completion (NO in step 108),the ECU 20 determines that the restart of the engine 21 has not beencompleted yet. Then, the ECU 20 proceeds to step 109.

Upon determining that the engine speed Ne is equal to or lower than thesecond preset speed N2 so that the engine restart request occurs withthe engine speed Ne being within the third speed range RA3 (NO in step106), the ECU 20 determines that the pinion 13 is allowed to be smoothlymeshed with the ring gear 23 without the rotational speed of the pinion13 being brought closer to that of the ring gear 23 because the RPM ofthe ring gear 23 is relatively low. Then, the ECU 20 proceeds to step109.

In step 109, the ECU 20 shifts its operation mode to the third restartcontrol mode, and carries out the third restart control task in step109.

Specifically, in step 109 a, the ECU 20 drives the electromagneticactuator 14 to shift the pinion 13 toward the ring gear 23 so that thepinion 13 is meshed with the ring gear 23. In step 109 b, after orduring the engagement of the pinion 13 with the ring gear 23, the ECU 20rotatably drives the starter motor 12 to rotate the pinion 13. Thiscranks the crankshaft 22 of the engine 21 to thereby restart the engine21.

Next, the ECU 20 proceeds to step 110, and determines whether therestart of the engine 21 has been completed in step 110 in the samemanner as step 105.

Upon determining that the restart of the engine 21 has not beencompleted yet (NO in step 110), the ECU 20 determines that the restartof the engine 21 has not been completed yet. Then, the ECU 20 returns tostep 109 and repeatedly executes the operations in steps 109 and 110.

Otherwise, upon determining that the restart of the engine 21 has beencompleted (YES in step 110), the ECU 20 exits the engine restart controlsubroutine R2 and returns to the main routine R1.

As described above, the engine starting system 1 according to the firstembodiment is designed to, during the engine-speed drop period by theautomatic stop of the engine 21, carry out:

the first restart control task when the engine restart request occurswith the engine speed Ne being within the first speed range RA1;

the second restart control task when the engine restart request occurswith the engine speed Ne being within the second speed range RA2; and

the third restart control task when the engine restart request occurswith the engine speed Ne being within the third speed range RA3.

The first restart control task restarts the ignition and/or thefuel-injection for each cylinder without cranking the crankshaft 22 bythe starter 11, thus automatically restarting the engine 21.

After the monitored rotational speed of the pinion 13 becomes close tothat of the ring gear 23, the second restart control task drives theelectromagnetic actuator 14 to mesh the pinion 13 with the ring gear 23to thereby crank the crankshaft 22 of the engine 21 to thereby restartthe engine 21.

The third restart control task drives the electromagnetic actuator 14 tomesh the pinion 13 with the ring gear 23. After or during the engagementof the pinion 13 with the ring gear 23, rotatably drives the startermotor 12 with the pinion 13 to crank the crankshaft 22 of the engine 21,thus restarting the engine 21.

The configuration of the engine starting system 1 makes it possible tocarry out any one of the first to third engine restart tasks that ismost suitable for the engine speed Ne at the moment when the enginerestart request occurs during the engine-speed drop period. Thisachieves an advantage of preventing or reducing noises and impacts fromoccurring due to the engagement of the pinion 13 with the ring gear 23and an advantage of reducing the power consumption of the starter 11.

In addition, the engine starting system 1 according to the firstembodiment is designed to estimate the engine speed (rotational speed ofthe ring gear 23) based on the elapsed time since the occurrence of theengine automatic stop request or the stop of the burning of the air-fuelmixture. This eliminates the need to provide a crank angle sensor with ahigh cost for measuring the engine speed with high accuracy. Similarly,the engine starting system 1 according to the first embodiment isdesigned to estimate the rotational speed of the pinion 13 based on theenergization duration of the starter motor 12 and the amount of currentto be applied thereto. This eliminates the need to provide a rotationalspeed sensor with a high cost for measuring the rotational speed of thepinion 13.

Thus, the engine starting system 1 according to the first embodimentmeets the low-cost requirements for vehicles as recent importanttechnical requirements.

Second Embodiment

A starting system for an internal combustion engine installed in avehicle according to the second embodiment of the present invention willbe described hereinafter with reference to FIG. 7.

The hardware and software structures of the engine starting systemaccording to the second embodiment are substantially identical to thoseof the engine starting system 1 according to the first embodiment exceptfor the following points. So, like parts between the engine startingsystems according to the first and second embodiments, to which likereference characters are assigned, are omitted or simplified indescription.

The ECU 20 of the engine starting system according to the secondembodiment is configured to execute an engine restart control subroutineillustrated in FIG. 7, which is different from the engine restartcontrol subroutine R2.

Specifically, upon determining that the engine speed Ne is higher thanthe second preset speed N2 so that the engine restart request occurswith the engine speed Ne being within the second speed range RA2, theECU 20 shifts its operation mode to the second restart control mode, andcarries out a second restart control task different from the secondrestart control task in step 107 of FIG. 6.

The second restart control task according to the second embodiment isdesigned to wait for the cranking of the crankshaft 22 by the starter 11even if the engine restart request occurs. Thereafter, when the enginespeed Ne falls within the third speed range RA3, the second restartcontrol task according to the second embodiment is designed to drive theelectromagnetic actuator 14 to mesh the pinion 13 with the ring gear 23,and, after or during the engagement of the pinion 13 with the ring gear23, rotatably drive the starter motor 12 with the pinion 13 to crank thecrankshaft 22 of the engine 21, thus restarting the engine 21.

Next, an engine restart control task to be executed by the ECU 20 inaccordance with the engine restart control subroutine according to thesecond embodiment illustrated in FIG. 7 will be described hereinafter.The engine restart control subroutine according to the second embodimentis repeatedly called in a given cycle during execution of the engineautomatic stop-and-start control routine R1.

When the engine restart control subroutine is called, the ECU 20determines whether the engine restart request occurs during the engine21 being under the automatic stop control in steps 101 and 102.

Upon determining that the engine restart request occurs (YES in step102), the ECU 20 proceeds to step 103 and determines whether the enginespeed Ne is higher than the first preset speed N1 to thereby determinewhether the engine speed Ne is within the first speed range RA1.

When it is determined that the engine speed Ne is higher than the firstpreset speed N1 so that the engine restart request occurs with theengine speed Ne being within the first speed range RA1 (YES in step103), the ECU 20 controls the ignition system 53 and/or the fuelinjection system 55 to restart the ignition and/or the fuel-injectionfor each cylinder without cranking the crankshaft 22 by the starter 11,thus automatically restarting the engine 21 in steps 104 and 105.

Otherwise, when it is determined that the engine speed Ne is equal to orlower than the first preset speed N1 (NO in step 103), the ECU 20proceeds to step 106 a. In step 106 a, the ECU 20 determines whether theengine speed Ne is equal to or lower than the second preset speed N2.

When it is determined that the engine speed Ne is higher than the secondpreset speed N2 so that the engine restart request occurs with theengine speed Ne being within the second speed range RA2 (NO in step 106a), the ECU 20 waits for the cranking of the crankshaft 22 by thestarter 11 while repeatedly determining whether the engine speed Ne isequal to or lower than the second preset speed N2.

As a result of one or more executions of the determining operation instep 106 a, when it is determined that the engine speed Ne is equal toor lower than the second preset speed N2 so that the engine speed Nedecreases within the third speed range RA3 (YES in step 106 a), the ECU20 proceeds to step 107A.

In step 107A, the ECU 20 shifts its operation mode to the second restartcontrol mode, and carries out the second restart control task accordingto the second embodiment.

Specifically, in step 107A, the ECU 20 drives the electromagneticactuator 14 to shift the pinion 13 toward the ring gear 23 so that thepinion 13 is meshed with the ring gear 23 as well as the operation instep 109 a. In step 107A, after or during the engagement of the pinion13 with the ring gear 23, the ECU 20 rotatably drives the starter motor12 to rotate the pinion 13 as well as the operation in step 109 b. Thiscranks the crankshaft 22 of the engine 21 to thereby restart the engine21.

Otherwise, when it is determined that the engine speed Ne is equal to orlower than the second preset speed N2 at the occurrence of the enginerestart request, in other words, the engine restart request occurs withthe engine speed Ne being within the third speed range RA3 (YES in step106 a), the ECU 20 proceeds to step 107A.

In step 107A, the ECU 20 shifts its operation mode to the third restartcontrol mode, and carries out the third restart control task.

Specifically, in step 107A, the ECU 20 drives the electromagneticactuator 14 to shift the pinion 13 toward the ring gear 23 so that thepinion 13 is meshed with the ring gear 23 as well as the operation instep 109 a. In step 107A, after or during the engagement of the pinion13 with the ring gear 23, the ECU 20 rotatably drives the starter motor12 to rotate the pinion 13 as well as the operation in step 109 b. Thiscranks the crankshaft 22 of the engine 21 to thereby restart the engine21.

Next, the ECU 20 proceeds to step 108, and determines whether therestart of the engine 21 has been completed in step 108 in the samemanner as step 105.

Upon determining that the engine speed Ne does not exceed the presetspeed for determination of restart completion (NO in step 108), the ECU20 determines that the restart of the engine 21 has not been completedyet. Then, the ECU 20 returns to step 107 a and continuously executesthe corresponding second or third engine restart control task.

As a result of one or more continuous executions of the correspondingsecond or third engine restart control task, when it is determined thatthe restart of the engine 21 has been completed, the ECU 20 exits theengine restart control subroutine according to the second embodiment.

As described above, the engine starting system according to the secondembodiment is designed to wait for the cranking of the crankshaft 22 bythe starter 11 even if the engine restart request occurs with the enginespeed Ne being within the second speed range RA2.

Thereafter, when the engine speed Ne falls within the third speed rangeRA3, the engine starting system according to the second embodiment isdesigned to drive the electromagnetic actuator 14 to mesh the pinion 13with the ring gear 23, and, after or during the engagement of the pinion13 with the ring gear 23, rotatably drive the starter motor 12 with thepinion 13 to crank the crankshaft 22 of the engine 21, thus restartingthe engine 21.

Thus, even if the engine restart request occurs with the engine speed Nebeing within the second speed range RA2, it is possible to omit theoperations to bring the rotational speed of the pinion 13 closer to thatof the ring gear 23, thus simplifying the engine restart control taskwhile reducing the power consumption of the starter 11. As describedabove, the engine starting system according to the second embodimentstarts the cranking of the crankshaft 22 by the starter 11 after a giventime has elapsed since the occurrence of the engine restart request withthe engine speed Ne being within the second speed range RA2. Because itis shown empirically that the time required for the engine speed Nepasses through the second speed range RA2 is relatively short, it ispossible to maintain, within an allowable range, the delay time elapsedfrom the occurrence of the engine restart request to the restart of theengine 21.

Third Embodiment

A starting system for an internal combustion engine installed in avehicle according to the third embodiment of the present invention willbe described hereinafter with reference to FIGS. 8 and 9.

The hardware and software structures of the engine starting systemaccording to the third embodiment are substantially identical to thoseof the engine starting system 1 according to the first embodiment exceptfor the following points. So, like parts between the engine startingsystems according to the first and third embodiments, to which likereference characters are assigned, are omitted or simplified indescription.

The ECU 20 of the engine starting system according to the thirdembodiment is configured to execute an engine restart control subroutineillustrated in FIG. 9 described hereinafter, which is different from theengine restart control subroutine R2.

In the third embodiment, the ECU 20 is configured to select, in additionto the first to third restart control modes, a fourth restart controlmode.

Specifically, referring to FIG. 8, during the engine-speed drop periodby the automatic stop of the engine 21, when the engine speed Nedecreases to the third preset speed N3 without the engine restartrequest occurring, the ECU 20 shifts its operation mode to the fourthrestart control mode, and carries out a fourth restart control task inthe fourth restart control mode.

Specifically, in the fourth restart control mode, the ECU 20 drives theelectromagnetic actuator 14 to shift the rotating pinion 13 toward thering gear 23 so that the rotating pinion 13 is pre-engaged with the ringgear 23 prior to the occurrence of the engine restart request.

After the pre-engagement of the pinion 13 with the ring gear 23, the ECU20 waits for the occurrence of the engine restart request.

When the engine restart request occurs, the ECU 20 drives the switchingelement 24 to turn it on, thus energizing the solenoid 25 a. Thisrotatably drives the starter motor 12 to rotate the pinion 13pre-engaged with the ring gear 23. This cranks the crankshaft 22 of theengine 21 to thereby restart the engine 21.

Next, an engine restart control task to be executed by the ECU 20 inaccordance with the engine restart control subroutine according to thethird embodiment illustrated in FIG. 9 will be described hereinafter.The engine restart control subroutine according to the third embodimentis repeatedly called in a given cycle during execution of the engineautomatic stop-and-start control routine R1.

When the engine restart control subroutine is called, the ECU 20determines the engine 21 is under the automatic stop control after thestop of burning of the air-fuel mixture in each cylinder in step 101.

Upon determining that the engine 21 is not under the automatic stopcontrol (NO in step 101), the ECU 20 exits the engine restart controlsubroutine R2 without executing the following steps 102 to 110, andreturns to the main routine R1.

Otherwise, upon determining that the engine 21 is under the automaticstop control (YES in step 101), the ECU 20 determines whether the enginespeed Ne is higher than the third preset speed N3, such as 100 rpm inthe third embodiment, in step 101 a.

Upon determining that the engine speed Ne is higher than the thirdpreset speed N3 (YES in step 101 a), the ECU 20 determines whether theengine restart request occurs in step 102, and upon determining that theengine restart request occurs (YES in step 102), the ECU 20 proceeds tostep 103. In step 103, the ECU 20 determines whether the engine speed Neis higher than the first preset speed N1 to thereby determine whetherthe engine speed Ne is within the first speed range RA1.

When it is determined that the engine speed Ne is higher than the firstpreset speed N1 so that the engine restart request occurs with theengine speed Ne being within the first speed range RA1 (YES in step103), the ECU 20 controls the ignition system 53 and/or the fuelinjection system 55 to restart the ignition and/or the fuel-injectionfor each cylinder without cranking the crankshaft 22 by the starter 11,thus automatically restarting the engine 21 in steps 104 and 105.

Otherwise, when it is determined that the engine speed Ne is equal to orlower than the first preset speed N1 (NO in step 103), the ECU 20proceeds to step 106. In step 106, the ECU 20 determines whether theengine speed Ne is higher than the second preset speed N2 to therebydetermine whether the engine speed Ne is within the second speed rangeRA2 or the third speed range RA3.

Upon determining that the engine speed Ne is higher than the secondpreset speed N2 so that the engine restart request occurs with theengine speed Ne being within the second speed range RA2 (YES in step106), the ECU 20 carries out the second restart control task in thesecond restart control mode.

Specifically, in the second restart control mode, the ECU 20 rotatablydrives the starter motor 12 to thereby rotate the pinion 13, and, afterthe monitored rotational speed of the pinion 13 becomes close to that ofthe ring gear 23, drives the electromagnetic actuator 14 to shift therotating pinion 13 toward the ring gear 23 so that the rotating pinion13 is meshed with the ring gear 23 (in steps 107 and 108). Theengagement of the rotating pinion 13 with the ring gear 23 cranks thecrankshaft 22 of the engine 21 to thereby restart the engine 21.

Otherwise, upon determining that the engine speed Ne is equal to orlower than the second preset speed N2 so that the engine restart requestoccurs with the engine speed Ne being within the third speed range RA3(NO in step 106), the ECU 20 carries out the third restart control taskin the third restart control mode.

Specifically, in the third restart control mode, the ECU 20 drives theelectromagnetic actuator 14 to shift the pinion 13 toward the ring gear23 so that the pinion 13 is meshed with the ring gear 23, and after orduring the engagement of the pinion 13 with the ring gear 23, rotatablydrives the starter motor 12 to rotate the pinion 13 in steps 109 and110. This cranks the crankshaft 22 of the engine 21 to thereby restartthe engine 21.

On the other hand, when it is determined that the engine speed Ne isequal to or lower than the third preset speed N3 (NO in step 101 a), theECU 20 determines that the engine speed Ne decreases to the third presetspeed N3 or below it without the engine restart request occurring. Then,the ECU 20 proceeds to step 111. In step 111, the ECU 20 shifts itsoperation mode to the fourth restart control mode, and carries out thefourth restart control task.

Specifically, in step 111 a, the ECU 20 drives the electromagneticactuator 14 to shift the rotating pinion 13 toward the ring gear 23 sothat the rotating pinion 13 is pre-engaged with the ring gear 23 priorto the occurrence of the engine restart request.

After the pre-engagement of the pinion 13 with the ring gear 23, the ECU20 waits for the occurrence of the engine restart request in step 111 b.

When the engine restart request occurs, the ECU 20 drives the switchingelement 24 to turn it on, thus energizing the solenoid 25 a in step 111c. This rotatably drives the starter motor 12 to rotate the pinion 13 instep 111 c. This cranks the crankshaft 22 of the engine 21 to therebyrestart the engine 21.

As described above, the engine starting system according to the thirdembodiment is designed to, during the engine-speed drop period by theautomatic stop of the engine 21, carry out the fourth restart controltask in the fourth restart control mode when the engine speed Nedecreases to the third preset speed N3 without the engine restartrequest occurring.

Specifically, the engine starting system according to the thirdembodiment is designed to shift the rotating pinion 13 toward the ringgear 23 so that the rotating pinion 13 is pre-engaged with the ring gear23 prior to the occurrence of the engine restart request.

The configuration allows the pinion 13 to be pre-engaged with the ringgear 23 before the engine-speed oscillation period, thus preventing thepinion 13 from being meshed within the engine-speed oscillation period.This makes it possible to prevent breakage of the starter 11 due to theengagement of the pinion 13 with the ring gear 23 within theengine-speed oscillation period. In addition, this makes it possible toprevent noises and impacts from occurring due to the engagement of thepinion 13 with the ring gear 23 within the engine-speed oscillationperiod.

After the pre-engagement of the pinion 13 to the ring gear 23 prior tothe occurrence of the engine restart request, when the engine restartrequest occurs, the ECU 20 works to rotatably drive the starter motor 12with the pinion 13 to crank the crankshaft 22, thus restarting theengine 21, making it possible to immediately restart the engine 21 inresponse to the occurrence of the engine restart request.

Note that the engine restart control subroutine according to the thirdembodiment is designed to cause the ECU 20 to execute the combination ofthe first to third restart control tasks according to the firstembodiment and the forth restart control task. The engine restartcontrol subroutine according to the third embodiment can be designed tocause the ECU 20 to execute the combination of the first to thirdrestart control tasks according to the second embodiment and the forthrestart control task.

Fourth Embodiment

A starting system for an internal combustion engine installed in avehicle according to the fourth embodiment of the present invention willbe described hereinafter with reference to FIGS. 10 and 11.

The hardware and software structures of the engine starting systemaccording to the fourth embodiment are substantially identical to thoseof the engine starting system 1 according to the first embodiment exceptfor the following points. So, like parts between the engine startingsystems according to the first and fourth embodiments, to which likereference characters are assigned, are omitted or simplified indescription.

The ECU 20 of the engine starting system according to the fourthembodiment is configured to execute an engine restart control subroutineillustrated in FIG. 11 described hereinafter, which is different fromthe engine restart control subroutine R2.

Specifically, referring to FIG. 10, during the engine-speed drop periodby the automatic stop of the engine 21, even if the engine restartrequest occurs with the engine speed Ne being greater than the thirdpreset speed N3, the ECU 20 waits for the execution of the enginerestart control subroutine.

In addition, during the engine-speed drop period by the automatic stopof the engine 21, when the engine speed Ne decreases to, the thirdpreset speed N3, the ECU 20 shifts its operation mode to the fourthrestart control mode, and carries out a fourth restart control task inthe fourth restart control mode.

Specifically, in the fourth restart control mode, during theengine-speed drop period by the automatic stop of the engine 21, whenthe engine speed Ne decreases to the third preset speed N3 at time t5,the ECU 20 energizes the electromagnetic actuator 14 to shift therotating pinion 13 toward the ring gear 23 so that the rotating pinion13 is preset to be meshed with the ring gear 23.

When the engine restart request has not occurred yet before the pinionpreset and a predetermined time required to complete the full engagementof the pinion 13 with the ring gear 23 has elapsed at time t6 since theenergization of the electromagnetic actuator 14, the ECU 20 determinesthat the engagement of the pinion 13 with the ring gear 23 is maintainedeven if the electromagnetic actuator 14 is deenergized, thusdeenergizing the electromagnetic actuator 14. Thereafter, when theengine restart request occurs, the ECU 20 drives the switching element24 to turn it on, thus energizing the solenoid 25 a. This rotatablydrives the starter motor 12 to rotate the pinion 13. This cranks thecrankshaft 22 of the engine 21 to thereby restart the engine 21.

Otherwise, when the engine restart request has occurred before thepinion preset, the ECU 20 immediately drives the switching element 24 toturn it on, thus energizing the solenoid 25 a. This rotatably drives thestarter motor 12 to rotate the pinion 13. This cranks the crankshaft 22of the engine 21 to thereby restart the engine 21.

Next, an engine restart control task to be executed by the ECU 20 inaccordance with the engine restart control subroutine according to thefourth embodiment illustrated in FIG. 11 will be described hereinafter.The engine restart control subroutine according to the fourth embodimentis repeatedly called in a given cycle during execution of the engineautomatic stop-and-start control routine R1.

When the engine restart control subroutine is called, the ECU 20determines whether the engine 21 is under the automatic stop controlafter the stop of burning of the air-fuel mixture in each cylinder instep 201.

Upon determining that the engine 21 is not under the automatic stopcontrol (NO in step 201), the ECU 20 repeatedly carries out thedetermination in step 201.

Thereafter, upon determining that the engine 21 is under the automaticstop control (YES in step 201), the ECU 20 determines whether the enginespeed Ne is equal to or lower than the third preset speed N3, such as100 rpm in the fourth embodiment, in step 202.

Upon determining that the engine speed Ne is higher than the thirdpreset speed N3 (NO in step 202), the ECU 20 repeatedly carries out thedetermination in step 202.

Thereafter, upon determining that the engine speed Ne is equal to lowerthan the third preset speed N3 (YES in step 202), the ECU 20 determinesthat the engine speed Ne decreases to the third preset speed N3 or belowit. Then, the ECU 20 proceeds to step 203. In step 203, the ECU 20shifts its operation mode to the fourth restart control mode, andcarries out the fourth restart control task.

Specifically, in step 203 a, the ECU 20 energizes the electromagneticactuator 14 to shift the rotating pinion 13 toward the ring gear 23 sothat the rotating pinion 13 is pre-engaged with the ring gear 23.

When the engine restart request has not occurred yet before the pinionpreset and the predetermined time required to complete the fullengagement of the pinion 13 with the ring gear 23 has elapsed since theenergization of the electromagnetic actuator 14, the ECU 20 determinesthat the engagement of the pinion 13 with the ring gear 23 is maintainedeven if the electromagnetic actuator 14 is deenergized, thusdeenergizing the electromagnetic actuator 14 in step 203 b. Thereafter,when the engine restart request occurs, the ECU 20 drives the switchingelement 24 to turn it on, thus energizing the solenoid 25 a in step 203c. This rotatably drives the starter motor 12 to rotate the pinion 13 in203 c. This cranks the crankshaft 22 of the engine 21 to thereby restartthe engine 21.

Otherwise, when the engine restart request has occurred before thepinion preset, the ECU 20 immediately drives the switching element 24 toturn it on, thus energizing the solenoid 25 a in step 203 d. Thisrotatably drives the starter motor 12 to rotate the pinion 13 in 203 d.This cranks the crankshaft 22 of the engine 21 to thereby restart theengine 21.

As described above, the engine starting system according to the fourthembodiment is designed to, when the engine speed Ne decreases to thethird preset speed N3, energize the electromagnetic actuator 14 to shiftthe rotating pinion 13 toward the ring gear 23 so that the rotatingpinion 13 is pre-energized with the ring gear 23.

When the engine restart request has not occurred yet before the pinionpreset and the predetermined time has elapsed since the energization ofthe electromagnetic actuator 14, the ECU 20 deenergizes theelectromagnetic actuator 14. Thus, the ECU 20 maintains the deenergizedstate of the electromagnetic actuator 14 before the occurrence of theengine restart request, making it possible to reduce the powerconsumption of the starter 11.

Note that in the third embodiment, the engine starting system can beprogrammed to:

energize the electromagnetic actuator 14 to shift the rotating pinion 13toward the ring gear 23 so that the rotating pinion 13 is pre-energizedwith the ring gear 23; and

when the engine restart request has not occurred yet before the pinionpreset and the predetermined time has elapsed since the energization ofthe electromagnetic actuator 14, deenergize the electromagnetic actuator14.

The engine starting system according to the third or fourth embodimentcan be equipped with a sensor 71 illustrated by phantom lines in FIG. 1;this sensor 71 is electrically connected to the ECU 20 and arranged tocheck whether the pinion 13 is fully engaged with the ring gear 23. Thatis, the ECU 20 according to the third or fourth embodiment can beprogrammed to deenergize the electromagnetic actuator 14 when dataindicative of the full engagement of the pinion 13 and the ring gear 23is sent from the sensor 71 without measuring the predetermined time.

Fifth Embodiment

A starting system for an internal combustion engine installed in avehicle according to the fifth embodiment of the present invention willbe described hereinafter with reference to FIGS. 12 and 13.

The hardware and software structures of the engine starting systemaccording to the fifth embodiment are substantially identical to thoseof the engine starting system 1 according to the first embodiment exceptfor the following points. So, like parts between the engine startingsystems according to the first and fifth embodiments, to which likereference characters are assigned, are omitted or simplified indescription.

The ECU 20 of the engine starting system according to the fifthembodiment is configured to execute an engine restart control subroutineillustrated in FIG. 13 described hereinafter, which is different fromthe engine restart control subroutine R2.

Specifically, referring to FIG. 12, during the engine-speed drop periodby the automatic stop of the engine 21, the ECU 20 is programmed toselect one of predetermined second and third restart control modes basedon the engine speed after the automatic stop of the engine 21 withoutselecting the first restart control mode.

Next, an engine restart control task to be executed by the ECU 20 inaccordance with the engine restart control subroutine according to thefifth embodiment illustrated in FIG. 13 will be described hereinafter.The engine restart control subroutine according to the fifth embodimentis repeatedly called in a given cycle during execution of the engineautomatic stop-and-start control routine R1.

When the engine restart control subroutine is called, the ECU 20determines whether the engine restart request occurs during the engine21 being under automatic stop control in steps 301 and 302 equivalent tosteps 101 and 102.

Upon determining that the engine restart request occurs (YES in step302), the ECU 20 proceeds to step 303 and determines whether the enginespeed Ne is equal to or lower than the first preset speed N1 to therebydetermine whether the engine speed Ne is within the first speed rangeRA1 in step 303.

When it is determined that the engine speed Ne is higher than the firstpreset speed N1 so that the engine restart request occurs with theengine speed Ne being within the first speed range RA1 (NO in step 303),the ECU 20 repeatedly carries out the determination without carrying outthe first restart control task in step 303.

Thereafter, when it is determined that the engine speed Ne is equal toor lower than the first preset speed N1 (YES in step 303), the ECU 20proceeds to step 304. In step 304, the ECU 20 determines whether theengine speed Ne is higher than the second preset speed N2.

Upon determining that the engine speed Ne is higher than the secondpreset speed N2 (YES in step 304), the ECU 20 proceeds to step 305.

In steps 305 and 306 equivalent to steps 107 and 108, the ECU 20 shiftsits operation mode to the second restart control mode, and carries outthe second restart control task.

Specifically, the ECU 20 drives the electromagnetic actuator 14 to shiftthe pinion 13 toward the ring gear 23 so that the pinion 13 is meshedwith the ring gear 23 in step 305 a. After or during the engagement ofthe pinion 13 with the ring gear 23, the ECU 20 rotatably drives thestarter motor 12 to rotate the pinion 13 in step 305 b. This cranks thecrankshaft 22 of the engine 21 to thereby restart the engine 21.

Otherwise, upon determining that the engine speed Ne is equal to orlower than the second preset speed N2 so that the engine restart requestoccurs with the engine speed Ne being within the third speed range RA3(NO in step 304), the ECU 20 proceeds to step 307. In steps 307 and 308equivalent to steps 109 and 110, the ECU 20 shifts its operation mode tothe third restart control mode, and carries out the third restartcontrol task in the third restart control mode.

Specifically, the ECU 20 drives the electromagnetic actuator 14 to shiftthe pinion 13 toward the ring gear 23 so that the pinion 13 is meshedwith the ring gear 23 in step 307 a, and after or during the engagementof the pinion 13 with the ring gear 23, rotatably drives the startermotor 12 to rotate the pinion 13 in step 307 b. This cranks thecrankshaft 22 of the engine 21 to thereby restart the engine 21.

As described above, the engine starting system according to the fifthembodiment makes it possible to carry out any one of the second andthird engine restart tasks that is most suitable for the engine speed Neat the moment when the engine restart request occurs during theengine-speed drop period. This achieves an advantage of preventing orreducing noises and impacts from occurring due to the engagement of thepinion 13 with the ring gear 23 and an advantage of reducing the powerconsumption of the starter 11.

Note that the engine restart control subroutine according to the fifthembodiment can be designed to cause the ECU 20 to execute thecombination of the second and third restart control tasks according tothe second embodiment.

When the engine restart request occurs with the monitored engine speedNe being within the engine-speed drop period or the engine-speedoscillation period, after the monitored difference in rotational speedbetween the ring gear 23 and the pinion 13 naturally falls within arange of ±250 rpm, the ECU 20 can carry out the operation in steps 109 aand 109 b as a first modification of each of the first to fifthembodiments.

Specifically, the ECU 20 according to the first modification drives theelectromagnetic actuator 14 to shift the pinion 13 toward the ring gear23 so that the pinion 13 is meshed with the ring gear 23 (see step 109a). After or during the engagement of the pinion 13 with the ring gear23, the ECU 20 according to the first modification rotatably drives thestarter motor 12 to rotate the pinion 13. This cranks the crankshaft 22of the engine 21 to thereby restart the engine 21 (see step 1094

When the engine restart request occurs with the monitored engine speedNe being within the engine-speed drop period or the engine-speedoscillation period, after the monitored difference in rotational speedbetween the ring gear 23 and the pinion 13 falls within a range of ±250rpm by rotatable drive of the pinion 13, the ECU 20 can be programmed tocarry out the operation in step 107 b as a second modification of eachof the first to fifth embodiments.

Specifically, the ECU 20 according to the second modification drives theelectromagnetic actuator 14 to shift the rotating pinion 13 toward thering gear 23 so that the rotating pinion 13 is meshed with the ring gear23, thus restarting the engine 21 (see step 107 b).

Both the first and second modifications can prevent or reduce noises andimpacts due to the engagement. In addition, the measurement accuracy ofthe rotational speeds of the pinion 13 and the ring gear 23 need not behigh. This eliminates the need to provide a rotational speed sensor witha high cost for measuring the rotational speed of the pinion 13.

Thus, the engine starting system according to each of the first andsecond modifications meets the low-cost requirements for vehicles asrecent important technical requirements.

The engine starting system with the one-way clutch 51 according to eachof the first to fifth embodiments can carry out the restart of theengine 21 when the engine restart request occurs with the monitoredengine speed Ne being within the engine-speed drop period or theengine-speed oscillation period.

Specifically, when the rotational speed of the ring gear 23 is higherthan that of the pinion 13, and the difference in rotational speedbetween the ring gear 23 and the pinion 13 is equal to or lower than apreset value of for example, 200 rpm (see step 400 in FIG. 14), theengine starting system can drive the electromagnetic actuator 14 toshift the pinion 13 toward the ring gear 23 so that the pinion 13 ismeshed with the ring gear 23 (see step 401). After or during theengagement of the pinion 13 with the ring gear 23, the engine startingsystem can rotatably drive the starter motor 12 to rotate the pinion 13.This cranks the crankshaft 22 of the engine 21 to thereby restart theengine 21 (see step 402).

The engine starting system according to each of the aforementionedembodiments and their modifications can be provided with a crank anglesensor included in the sensors 59. The crank angle sensor is operativeto measure a rotational angular position of the crankshaft 22 relativeto a reference position every time the crankshaft 22 is rotated by apreset angle. The crank angle sensor is operative to output, to the ECU20, the measured data (measured rotational angular position). Based onthe measured data sent from the crank angle sensor, the ECU 20 canobtain the engine speed Ne.

The engine starting system according to each of the aforementionedembodiments and their modifications can be provided with a rotationalspeed sensor included in the sensors 59 and operative to measure therotational angle of the pinion 13. The rotational angle sensor isoperative to output, to the ECU 20, the measured rotational angle. Basedon the measured data sent from the crank angle sensor, the ECU 20 canobtain the rotational angle of the pinion 13.

While there has been described what is at present considered to be theembodiments and their modifications of the present invention, it will beunderstood that various modifications which are not described yet may bemade therein, and it is intended to cover in the appended claims allsuch modifications as fall within the scope of the invention.

1. A system for restarting, according to an occurrence of an enginerestart request, an internal combustion engine that has beenautomatically controlled for stop thereof in response to an engineautomatic stop request, the internal combustion engine normally workingto burn fuel therein to rotate a crankshaft with a ring gear attachedthereto, the system comprising: a starter provided with a motor forrotatably driving an output shaft with a pinion and an actuator workingto shift the pinion toward the ring gear to be engaged with the ringgear; a monitor unit working to monitor a rotational speed of theinternal combustion engine, the rotational speed of the internalcombustion engine dropping by the automatic control for stop of theinternal combustion engine; and when the engine restart request occurswith the rotational speed being within a preset range during therotational speed of the internal combustion engine dropping by theautomatic control for stop of the internal combustion engine, a driveunit working to: drive the actuator to shift the pinion toward the ringgear to be engaged with the ring gear; and rotatably drive the motorwith the pinion being at least partly engaged with the ring gear tothereby crank the crankshaft of the internal combustion engine.
 2. Asystem for restarting, according to an occurrence of an engine restartrequest, an internal combustion engine that has been automaticallycontrolled for stop thereof in response to an engine automatic stoprequest, the internal combustion engine normally working to burn fueltherein to rotate a crankshaft with a ring gear attached thereto, thesystem comprising: a starter provided with a motor for rotatably drivingan output shaft with a pinion and an actuator working to shift thepinion toward the ring gear to be engaged with the ring gear; a monitorunit working to monitor a rotational speed of the internal combustionengine, the rotational speed of the internal combustion engine droppingby the automatic control for stop of the internal combustion engine; andan executing unit working to: select, based on the rotational speed ofthe internal combustion engine at a timing of the occurrence of theengine restart request, any one of a first restart task and a secondrestart task; execute, when the first restart task is selected, thefirst restart task to thereby: rotatably drive the motor, determinewhether the pinion is allowed to be rotated with the ring gear, andafter it is determined that the pinion is allowed to be rotated with thering gear, drive the actuator to shift the pinion toward the ring gearto be engaged with the ring gear to thereby crank the crankshaft of theinternal combustion engine; and execute, when the second restart task isselected, the second restart task to thereby: drive the actuator toshift the pinion toward the ring gear to be engaged with the ring gear,and rotatably drive the motor with the pinion being at least partlyengaged with the ring gear to thereby crank the crankshaft of theinternal combustion engine.
 3. The system according to claim 2, whereinthe executing unit works to select the first restart task when therotational speed of the internal combustion engine at the timing of theoccurrence of the engine restart request is equal to or lower than afirst preset speed and higher than a second preset speed, the secondpreset speed being lower than the first preset speed, and the executingunit works to select the second restart task when the rotational speedof the internal combustion engine at the timing of the occurrence of theengine restart request is equal to or lower than the second presetspeed.
 4. The system according to claim 3, wherein the executing unitworks to select, based on the rotational speed of the internalcombustion engine at the timing of the occurrence of the engine restartrequest, any one of the first restart task, the second restart task, anda third restart task, the executing unit working to: select the thirdrestart task when the rotational speed of the internal combustion engineat the timing of the occurrence of the engine restart request is higherthan the first preset speed; and execute, when the third restart task isselected, the third restart task to thereby: restart a burning of thefuel in the internal combustion engine, thus restarting the internalcombustion engine without cranking the crankshaft.
 5. The systemaccording to claim 2, wherein the executing unit works to monitor arotational speed of the pinion, and determine that the pinion is allowedto be rotated with the ring gear when a difference between therotational speed of the internal combustion engine and the rotationalspeed of the pinion is within ±250 rpm.
 6. The system according to claim5, wherein the executing unit works to determine that the pinion isallowed to be rotated with the ring gear when the difference between therotational speed of the internal combustion engine and the rotationalspeed of the pinion is within ±200 rpm.
 7. The system according to claim2, wherein the executing unit works to monitor a difference between afirst peripheral speed on a first pitch circle on the ring gear and asecond peripheral speed of a second pitch circle on the pinion, anddetermine that the pinion is allowed to be rotated with the ring gearwhen the difference between the first peripheral speed on the firstpitch circle on the ring gear and the second peripheral speed of thesecond pitch circle on the pinion is within ±3.1 meters per second. 8.The system according to claim 2, further comprising: a one-way clutchrotatably provided on the output shaft of the motor and designed to onlytransfer rotational motion of the ring gear to the pinion when thepinion is engaged with the ring gear, the executing unit working tomonitor a rotational speed of the pinion, and determine that the pinionis allowed to be rotated with the ring gear when the rotational speed ofthe internal combustion engine is higher than the rotational speed ofthe pinion and a difference between the rotational speed of the internalcombustion engine and the rotational speed of the pinion is equal to orlower than a preset value.
 9. The system according to claim 8, whereinthe executing unit works to determine that the pinion is allowed to berotated with the ring gear when a difference between the rotationalspeed of the internal combustion engine and the rotational speed of thepinion is within ±250 rpm.
 10. The system according to claim 9, whereinthe executing unit works to determine that the pinion is allowed to berotated with the ring gear when the difference between the rotationalspeed of the internal combustion engine and the rotational speed of thepinion is within ±200 rpm.
 11. The system according to claim 2, furthercomprising: a one-way clutch rotatably provided on the output shaft ofthe motor and designed to only transfer rotational motion of the ringgear to the pinion when the pinion is engaged with the ring gear, theexecuting unit working to monitor a difference between a firstperipheral speed on a first pitch circle on the ring gear and a secondperipheral speed of a second pitch circle on the pinion, and determinethat the pinion is allowed to be rotated with the ring gear when thedifference between the first peripheral speed on the first pitch circleon the ring gear and the second peripheral speed of the second pitchcircle on the pinion is within ±3.1 meters per second.
 12. The systemaccording to claim 2, wherein the executing unit works to select, basedon the rotational speed of the internal combustion engine at the timingof the occurrence of the engine restart request, any one of the firstrestart task, the second restart task, and a third restart task, theexecuting unit working to execute, when the third restart task isselected, the third restart task to thereby: restart a burning of thefuel in the internal combustion engine, thus restarting the internalcombustion engine without cranking the crankshaft, the executing unitworking to: select the third restart task when the rotational speed ofthe internal combustion engine at the timing of the occurrence of theengine restart request is higher than a first preset speed; wait whenthe rotational speed of the internal combustion engine at the timing ofthe occurrence of the engine restart request is equal to or lower thanthe first preset speed and higher than a second preset speed, the secondpreset speed being lower than the first preset speed; select the secondrestart task when the rotational speed of the internal combustion enginereaches equal to or below the second preset speed; and select the secondrestart task when the rotational speed of the internal combustion engineat the timing of the occurrence of the engine restart request is equalto or lower than the second preset speed.
 13. The system according toclaim 3, wherein the executing unit works to execute, when therotational speed of the internal combustion engine reaches a thirdpreset speed higher than zero and lower than the second preset speedwithout the engine restart request occurring, a fourth task to thereby:drive the actuator to shift the pinion toward the ring gear to beengaged with the ring gear; and when the engine restart request occursafter the engagement of the pinion with the ring gear, rotatably drivethe motor to thereby crank the crankshaft of the internal combustionengine.
 14. The system according to claim 3, wherein the internalcombustion engine is designed such that a behavior of the rotationalspeed of the internal combustion engine positively and negativelyoscillates after the rotational speed of the internal combustion enginehas first reached zero, and the executing unit works to execute, whenthe rotational speed of the internal combustion engine reaches a thirdpreset speed higher than zero and lower than the second preset speedwithout the engine restart request occurring, a fifth task to thereby:drive the actuator to shift the pinion toward the ring gear to beengaged with the ring gear; and when the engine restart request occursafter the engagement of the pinion with the ring gear, rotatably drivethe motor to thereby crank the crankshaft of the internal combustionengine.
 15. The system according to claim 3, wherein the first presetspeed is selected from a range of 300 to 700 rpm.
 16. The systemaccording to claim 3, wherein the second preset speed is selected from arange of 50 to 450 rpm.
 17. The system according to claim 1, wherein themonitor unit works to estimate, based on an elapsed time from any one ofthe occurrence of the engine automatic stop request and a stop of theburning of the fuel in the internal combustion engine, the rotationalspeed of the internal combustion engine.
 18. The system according toclaim 5, wherein the starter works to supply a current to the motor tothereby energize the motor, the energized motor rotatably driving theoutput shaft with the pinion, and the executing unit works to estimate,based on at least one of an energization duration of the motor and anamount of the current to be supplied to the motor, the rotational speedof the internal combustion engine.
 19. A system for restarting,according to an occurrence of an engine restart request, an internalcombustion engine that has been automatically controlled for stopthereof in response to an engine automatic stop request, the internalcombustion engine normally working to burn fuel therein to rotate acrankshaft with a ring gear attached thereto, the system comprising: astarter provided with a motor for rotatably driving an output shaft witha pinion and an actuator working to shift the pinion toward the ringgear to be engaged with the ring gear; a monitor unit working to monitora rotational speed of the internal combustion engine, the rotationalspeed of the internal combustion engine dropping by the automaticcontrol for stop of the internal combustion engine; and when therotational speed of the internal combustion engine reaches a presetspeed close to or higher than zero without the engine restart requestoccurring, a drive unit working to: drive the actuator to shift thepinion toward the ring gear to be engaged with the ring gear; and whenthe engine restart request occurs after the engagement of the pinionwith the ring gear, rotatably drive the motor to thereby crank thecrankshaft of the internal combustion engine.
 20. The system accordingto claim 19, wherein the internal combustion engine is designed suchthat a behavior of the rotational speed of the internal combustionengine positively and negatively oscillates after the rotational speedof the ring gear has first reached zero.
 21. The system according toclaim 19, wherein the drive unit works to: energize the actuator so asto drive the actuator, the driven actuator shifting the pinion towardthe ring gear to be engaged with the ring gear; and deenergize theactuator at least one of when a preset time has elapsed since theenergization of the actuator and when it is checked that the pinion isengaged with the ring gear.
 22. The system according to claim 20,wherein the preset time is an elapsed time since the energization of theactuator to a timing when the rotational speed of the internalcombustion engine becomes zero after the positive and negativeoscillation has been completed.
 23. A system for restarting, accordingto an occurrence of an engine restart request, an internal combustionengine that has been automatically controlled for stop thereof inresponse to an engine automatic stop request, the internal combustionengine normally working to burn fuel therein to rotate a crankshaft witha ring gear attached thereto, the system comprising: a starter providedwith a motor for rotatably driving an output shaft with a pinion and anactuator working to shift the pinion toward the ring gear to be engagedwith the ring gear; a monitor unit working to monitor a parameterassociated with a difference between a rotational speed of the internalcombustion engine and a rotational speed of the pinion, the rotationalspeed of the internal combustion engine dropping by the automaticcontrol for stop of the internal combustion engine, a behavior of therotational speed of the internal combustion engine positively andnegatively oscillating after the rotational speed of the internalcombustion engine has first reached zero; and when the engine restartrequest occurs at least one of: during the rotational speed of theinternal combustion engine dropping, and during the behavior of therotational speed of the internal combustion engine positively andnegatively oscillating, after the parameter has been within a presetrange, a drive unit working to: drive the actuator to shift the piniontoward the ring gear to be engaged with the ring gear; and rotatablydrive the motor with the pinion being at least partly engaged with thering gear to thereby crank the crankshaft of the internal combustionengine.
 24. The system according to claim 23, wherein the parameter isthe difference between the rotational speed of the internal combustionengine and the rotational speed of the pinion, and the preset range isset to be ±250 rpm.
 25. The system according to claim 23, wherein theparameter is a difference between a first peripheral speed on a firstpitch circle on the ring gear and a second peripheral sped of a secondpitch circle on the pinion, and the preset range is set to be ±3.1meters per second.
 26. A system for restarting, according to anoccurrence of an engine restart request, an internal combustion enginethat has been automatically controlled for stop thereof in response toan engine automatic stop request, the internal combustion enginenormally working to burn fuel therein to rotate a crankshaft with a ringgear attached thereto, the system comprising: a starter provided with amotor for rotatably driving an output shaft with a pinion and anactuator working to shift the pinion toward the ring gear to be engagedwith the ring gear; a monitor unit working to monitor a parameterassociated with a difference between a rotational speed of the internalcombustion engine and a rotational speed of the pinion, the rotationalspeed of the internal combustion engine dropping by the automaticcontrol for stop of the internal combustion engine, a behavior of therotational speed of the internal combustion engine positively andnegatively oscillating after the rotational speed of the internalcombustion engine has first reached zero; and when the engine restartrequest occurs at least one of: during the rotational speed of theinternal combustion engine dropping, and during the behavior of therotational speed of the internal combustion engine positively andnegatively oscillating, a drive unit working to: rotatably drive themotor to thereby rotate the pinion so that the monitored parameter hasbeen within a preset range; and drive the actuator to shift the piniontoward the ring gear to be engaged with the ring gear to thereby crankthe crankshaft of the internal combustion engine.
 27. The systemaccording to claim 26, wherein the parameter is the difference betweenthe rotational speed of the internal combustion engine and therotational speed of the pinion, further comprising: a one-way clutchrotatably provided on the output shaft of the motor and designed to onlytransfer rotational motion of the ring gear to the pinion when thepinion is engaged with the ring gear, the drive unit working to, whenthe engine restart request occurs during the rotational speed of theinternal combustion engine dropping, drive the actuator to shift thepinion toward the ring gear to be engaged with the ring gear to therebycrank the crankshaft of the internal combustion engine after therotational speed of the internal combustion engine is higher than therotational speed of the pinion and the difference between the rotationalspeed of the internal combustion engine and the rotational speed of thepinion is equal to or lower than 200 rpm.
 28. The system according toclaim 26, wherein the parameter is a difference between a firstperipheral speed on a first pitch circle on the ring gear and a secondperipheral sped of a second pitch circle on the pinion, and the presetrange is set to be ±3.1 meters per second.
 29. The system according toclaim 26, wherein the parameter is the difference between a firstperipheral speed on a first pitch circle on the ring gear and a secondperipheral sped of a second pitch circle on the pinion, furthercomprising: a one-way clutch rotatably provided on the output shaft ofthe motor and designed to only transfer rotational motion of the ringgear to the pinion when the pinion is engaged with the ring gear, thedrive unit working to, when the engine restart request occurs during therotational speed of the internal combustion engine dropping, drive theactuator to shift the pinion toward the ring gear to be engaged with thering gear to thereby crank the crankshaft of the internal combustionengine after the first peripheral speed on the first pitch circle on thering gear is higher than the second peripheral speed of the second pitchcircle on the pinion and the difference between the first peripheralspeed on the first pitch circle on the ring gear and the secondperipheral speed of the second pitch circle on the pinion is equal to orlower than 3.1 meters per second.
 30. The system according to claim 1,wherein the starter is designed to individually drive the motor and theactuator.